Difference Between Cyclic and Noncyclic Photophosphorylation

Difference Between Cyclic and Noncyclic Photophosphorylation Overview

Cyclic and noncyclic photophosphorylation are two processes involved in ATP synthesis during photosynthesis, particularly in the light-dependent reactions. Cyclic photophosphorylation occurs only in photosystem I. Noncyclic photophosphorylation occurs in both photosystem I and photosystem II.  In cyclic photophosphorylation, only ATP is produced. Noncyclic photophosphorylation produces ATP along with reduced coenzymes. Cyclic photophosphorylation serves primarily to produce ATP. Noncyclic photophosphorylation produces both ATP and reduced coenzymes. Both processes are essential for energy production in plants during photosynthesis, utilizing light energy to convert ADP and inorganic phosphate into ATP.

Difference Between Cyclic and Noncyclic Photophosphorylation in Tabular Form

The process of photosynthesis unfolds through two distinct phases: the light-dependent reactions and the light-independent reactions, commonly referred to as the dark reactions. During the light-dependent reactions, a process known as photophosphorylation takes place, wherein a phosphate group is added in the presence of light. Hence, it's termed photophosphorylation due to its light-dependent nature. Photophosphorylation can be categorized into two specific types: cyclic photophosphorylation and noncyclic photophosphorylation. Let's find out the key difference between Cyclic And noncyclic photophosphorylation:

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What is Cyclic Photophosphorylation?

Cyclic photophosphorylation involves a cyclic movement of electrons that leads to the production of ATP molecules. Within this mechanism, plant cells transform ADP into ATP, providing immediate energy for cellular functions. This process predominantly takes place in the thylakoid membrane, utilizing Photosystem I and Chlorophyll P700. In the cyclic photophosphorylation sequence, electrons are transferred back to the P700 from the electron acceptor rather than moving towards NADP. This movement facilitates the formation of ATP molecules. The electron transport chain in this process establishes a proton-motive force. This force pushes H+ ions across the membrane, generating a concentration gradient. Subsequently, this gradient activates ATP synthase through chemiosmosis. It's essential to note that cyclic photophosphorylation does not result in the production of oxygen or NADPH. Finally, through cyclic photophosphorylation, two ATP molecules are generated to meet the energy demands of the cell. 

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What is Noncyclic Photophosphorylation?

Noncyclic photophosphorylation involves the movement of electrons in a singular, noncyclic direction to produce ATP molecules, harnessing energy from the excited electrons provided by Photosystem II. This process earns its name, "noncyclic photophosphorylation," because the electrons discharged by Photosystem II's P680 are captured by Photosystem I's P700 and do not circle back to P680. Essentially, the electron movement in this process follows a unidirectional or noncyclic path. In the noncyclic photophosphorylation sequence, electrons released by P700 are transported by the primary acceptor, eventually transferring them to NADP. This mechanism results in the creation of 1 ATP and 2 NADPH2 molecules. The electrons combine with protons (H⁺) generated during the breakdown of water molecules, facilitating the reduction of NADP to NADPH. The equation illustrating this reaction is: NADP⁺ + 2H⁺ + 2e⁻ → NADPH + H⁺NADP⁺ + 2H⁺ + 2e⁻ → NADPH + H⁺ Whether you are a student eager to deepen your knowledge or someone simply curious about science, there is always room for growth and discovery.